1. Field of the Invention
Generally, the present disclosure relates to the fabrication of integrated circuits, and, more particularly, to techniques and systems for performing a UV (ultraviolet) treatment.
2. Description of the Related Art
Semiconductor devices and generally any type of microstructure devices are typically formed on specific substrates made of any appropriate material. During the very complex manufacturing sequence, a plurality of material layers are typically formed on the substrate and are subsequently treated, for instance, by etching one or more materials, implanting specific impurities, such as dopant species and the like, in order to obtain individual components having the desired characteristics. For example, semiconductive materials, insulating materials, highly conductive materials, such as metals and the like, are formed and may be patterned, for instance on the basis of sophisticated lithography techniques, in order to transfer a desired device layout from one or more lithography masks into the various material layers. Due to a continuous advance in many of the involved fabrication techniques, such as lithography, ion implantation, etching, planarizing, deposition of various material compositions and the like, the features sizes of the individual components have been reduced in order to enhance performance of these components and also to obtain an increased packing density so that more and more functions may be implemented into a single microstructure device. For example, in complex semiconductor devices, such as microprocessors of sophisticated configuration, several hundred millions of individual transistor elements may be provided in combination with the corresponding wiring network in order to provide the electrical connections between the individual circuit elements. To this end, several hundred individual process steps may typically be required to form a plurality of individual semiconductor chips on a single substrate, wherein each of these process steps has to be performed within specifically set process tolerances in order to obtain the final device characteristics. Consequently, in complex semiconductor devices or any other microstructure devices, critical dimensions of individual elements, such as field effect transistors, have reached the deep micron range wherein, currently, critical dimensions of 40 nm and less may be implemented in volume production techniques. In addition to reducing the critical dimensions of the individual semiconductor elements, also appropriate material systems may have to be used, for instance in the form of dielectric materials, conductive materials and the like. Moreover, the characteristics of these base materials may typically be adjusted on the basis of additional treatments in an attempt to enhance overall performance and reliability of complex semiconductor devices without unduly adding to the overall complexity of the manufacturing process.
For example, upon reducing the dimensions of transistor elements, thereby improving switching speed and drive current capability, the signal propagation delay may no longer be limited by the circuit elements in the transistor level but may also be strongly affected by the performance of a metallization system, which may typically be provided in the form of a plurality of stacked metallization layers, in which a network of highly conductive metal lines and vias may establish the required electrical connections. Well-established metallization systems are based on aluminum and silicon dioxide as conductive materials and interlayer dielectric materials, which, however, may no longer be appropriate for meeting the requirements of sophisticated integrated circuits. For this reason, aluminum is increasingly replaced by copper or copper alloys or other metals of superior conductivity, while at the same time the parasitic capacitance of the various metallization levels is reduced by steadily reducing the dielectric constant of the dielectric material that may electrically insulate the various conductive regions and which may provide a chemical and mechanical stability of the metallization system. Since well-approved dielectric materials, such as silicon dioxide, silicon nitride and the like, are considered inappropriate, a plurality of alternative materials have been developed in combination with associated deposition techniques in order to obtain an effective dielectric constant of approximately 3.0 and less, in which case these dielectric materials may be referred to as low-k dielectric materials. One important mechanism for reducing the dielectric constant of specific dielectric materials is the generation of a porous structure, which may be accomplished by incorporating specific components into the dielectric base material, which may subsequently be removed by treating the dielectric material. In this respect, a treatment on the basis of ultraviolet (UV) radiation has proven to be a very efficient mechanism in order to modify the characteristics of a dielectric material in view of reducing the dielectric constant.
A further example of efficiently modifying the characteristics of a dielectric base material by using UV radiation is the generation or adjustment of an internal stress level of specific dielectric materials, such as silicon nitride and the like, in order to appropriately adjust the characteristics of a circuit element, such as a transistor. For instance, it is well known that a certain type of strain in the channel region of a field effect transistor may efficiently modify the charge carrier mobility, which in turn directly translates into a modification of the drive current of the transistor. One efficient mechanism for inducing a strain component in the channel region of a field effect transistor is the provision of a dielectric material close to the transistor and the adjustment of the internal stress level of the material in accordance with device requirements. For instance, it has been recognized that the molecular structure of a silicon nitride material may be changed upon exposure to UV radiation, which may result in a removal of hydrogen, which in turn may result in a shift of an internal stress level towards a tensile stress. Upon depositing a tensile dielectric material, the internal stress level thereof may further be increased upon exposure to UV radiation.
Although the treatment on the basis of UV radiation represents a very efficient mechanism for appropriately adapting the characteristics of dielectric materials during the fabrication of complex semiconductor devices, it turns out that the final result of the UV treatment strongly depends on the process parameters, such as the irradiance of the radiation, that is, the radiative flux per unit area, the process temperature and the like. However, these process parameters may be difficult to control, as will be explained with reference to FIGS. 1a and 1b. 
FIG. 1a schematically illustrates a UV process tool 100, which is to be understood as a process tool in which one or more substrates may be exposed to UV radiation, which may typically be provided with a wavelength range of approximately 200-400 nm, depending on the specific application. The tool 100 typically comprises a process chamber 101, which represents any appropriate hardware component in order to receive a substrate 110 and to establish a desired process ambient, for instance on the basis of any appropriate gases, such as inert gases, reactive gases and the like. For this purpose, typically, well-known hardware resources, such as supply lines and exhaust lines (not shown), are provided in combination with gas flow rate controllers, gas resources and the like. Furthermore, the process tool 100 comprises a radiation source 103, which may typically emit one or more UV lengths, such as mercury vapor lamps and the like, which may be appropriately arranged so as to provide UV radiation 103A to the substrate 110. For example, the radiation source 103 may comprise any appropriate compartment or housing to establish the appropriate environmental conditions for the corresponding actual UV lamps, for instance by providing an appropriate cooling system and the like. Furthermore, any optical components, such as a silica cover and the like, may be provided in the radiation source 103 as required for appropriately positioning the source 103 and directing the radiation 103A to the substrate 110. For convenience, any such components are not shown, but these components are well known in the art. Moreover, the tool 100 may comprise a heater unit 102, which may also act as a substrate holder, depending on the configuration of the tool 100.
Upon operating the UV process tool 100, the substrate 110 is positioned within the process chamber 101, for instance on the heater unit 102, which in turn may be supplied with an appropriate input power 102A in order to establish a desired process temperature within the process chamber 101. Furthermore, the radiation source 103 may be operated by supplying power to the corresponding lamps or other radiation sources in accordance with a predefined parameter setting to obtain the radiation 103A having a specific wavelength composition and also a spatially predefined shape. For example, the radiation 103A may irradiate a specified surface area on the substrate 110, which may require a repositioning of the radiation 103A relative to the substrate 110 in order to completely treat the surface of the substrate 110. In other cases, the radiation source 103 is configured such that the substrate 110 as a whole may be irradiated, wherein the results of the treatment in the tool 100 may strongly depend on the exposure dose, the wavelength range used, the process temperature, the gaseous ambient in the chamber 101 and the like. For example, the substrate 110 may have formed thereon a dielectric material, such as a low-k dielectric material, wherein chemical bonds may be reconfigured upon being exposed to the radiation 103A so that a removal of certain species may be accomplished, which may finally result in a reduced dielectric constant. Thus, the dielectric constant of the resulting dielectric material may strongly depend on the overall process parameters, which in turn may significantly affect the electrical performance of the metallization systems and thus of the semiconductor devices. Since the process parameters, such as the process temperature, the gas flow rates and the like, may be controlled with a high degree of precision, a very important parameter represents the irradiance of the radiation 103A, since this value represents the energy deposition per unit area on the surface of the substrate 110 for a given distribution of the wavelength range emitted by the radiation source 103. Thus, the irradiance in combination with the exposure time and the effective wavelength range incident on the substrate 110 may strongly affect the result of the treatment in the process tool 100. For this reason, in many conventional UV process tools, a sensor element 104 is provided at an appropriate location within the process chamber 101 in order to obtain a monitor signal 104A that is indicative of the irradiance of the radiation source 103. It is well known that the irradiance may significantly vary over lifetime of UV radiation sources, for instance due to aging, failures in one or more of the hardware components of the radiation source 103, such as contamination of optical components and the like, so that the monitor signals 104A are obtained on a regular basis. It turns out, however, that the sensor elements 104 cover only a small area within the chamber 101 so that the signal 104A may not efficiently represent the integrated irradiance of the source 103. Moreover, currently available UV sensors may also suffer from a pronounced variability so that the long term stability of the UV measurement system itself may not be guaranteed, thereby making the currently available monitor systems for UV radiation tools based on the sensor 104 less than desirable, in particular for sophisticated manufacturing techniques requiring a high uniformity of the involved processes.
FIG. 1b schematically illustrates the substrate 110 according to other conventional strategies in determining the irradiance of the radiation source. In this case, a specific material layer 111 may be provided at least locally on the substrate 110 in order to detect the effect of the radiation 103A. For this purpose, dedicated test substrates or at least dedicated test sites on a substrate have to be provided and have to be examined in order to obtain a quantitative result with respect to a certain material characteristic caused by the momentary irradiance of the radiation 103A. For instance, the dielectric constant, mechanical stress, index of refraction, the density of the material or other mechanical parameters, the shrinkage of the material and the like may be determined on the basis of a corresponding metrology process and may then be used for assessing the status of the radiation 103A. In this case, however, in addition to processing the substrate 110, a further metrology process has to be performed, which may thus not allow a fast response to the tool 100 since, typically, at least a time interval of one hour or more may be required until the measurement result is obtained. In this time interval, the tool 100 may not be available or may be operated with a high risk of producing non-acceptable process results.
The present disclosure is directed to various methods and devices that may avoid, or at least reduce, the effects of one or more of the problems identified above.